Electronic circuit



March 15, 1966 N. 1'. NEAPOLITAKIS 3,240,199

ELECTRONIC CIRCUIT Filed May 23, 1963 FIG] DISTRIBUTOR TO DISTRIBUTORINVENTOR. NICHOLAS T. NEAPOLITAKIS United States Patent 3,240,199ELECTRONIC CIRCUIT Nicholas T. Neapolitakis, Chicago, 111., assignor toMotorola, Inc, Franklin Park, Ill., a corporation of Illinois Filed May23, 1963, Ser. No. 282,637 7 Claims. (Cl. 123-148) This inventionrelates to ignition systems for internal combustion engines, and moreparticularly to a transistorized ignition system for an internalcombustion engine having a positive ground electrical system.

In conventional ignition systems, a relatively large current is passedthrough a high voltage coil and interrupted by intermittently openingbreaker points, thereby causing a large voltage to be developed acrossthe coil and transmitted to the spark plugs. The voltage developeddepends upon the breaking of the current applied to the induction coil.

One of the most frequent causes of trouble in conventional ignitionsystems, especially those used with automobile engines, is pitting,carbonizing and wear of the contacts of the breaker points. This occursdue to the interruption of high voltage and current which causes arcingacross the points. Fitting, earbonizin-g and wear result in poorelectrical contact and eventual failure of the system. Automobile usersare normally required to replace the breaker points several times duringthe useful life of an automobile, even though condensers are generallyconnected in parallel with the breaker points to reduce arcing.

It has been proposed to interrupt the current through the spark coil byutilizing a transistor or a plurality of transistors, and controllingthe conduction of the transistor by a relatively small currentinterrupted by the breaker points. Such systems considerably prolong thelife of the breaker points by reducing the current passing therethrough.Certain problems arise, however, in incorporating such ignition systemsin automobile electrical systems wherein the positive side of the sourceof potential is directly connected to ground. This is because one sideof the breaker points is usually grounded, and if a PNP outputtransistor is connected to be switched by the breaker points, it will beturned oil? when the points are closed and on when the points areopened. This is opposite to the sequence of the usual ignition systems.

The problem set forth can be overcome by changing the timing system toprovide a new spark sequence, but this requires a major redesign of theengine. It would be possible to provide the desired sequence by the useof NPN transistors instead of PNP transistors, but at the present timeNPN transistors of the required power and voltage rating are notcommercially available. The proper timing sequence might be attained byuse of a pulse transformer which reverses the polarity in the secondarywinding, but this requires a very large pulse transformer forsatisfactory operation, raising the cost to a prohibitive level.

Accordingly, it is an object of this invention to provide an improvedpositive ground ignition system for internal combustion engines.

Another object of the invention is to provide a positive ground ignitionsystem suitable for replacing standard ignition systems with a minimumof alteration of existing apparatus.

Still another object of the invention is to provide a transistorizedignition system for positive ground electrical system utilizing PNPtransistors and avoiding the need for a pulse transformer.

A feature of the invention is the provision of an electronic ignitionsystem for internal combustion engines having positive ground electricalsystems, which ignition 3,249,199 Patented Mar. 15, 1966 system utilizesa cascade connected coupling transistor between the breaker points andthe output transistor so that the output transistor will be cut off whenthe breaker points open.

Another feature of the invention is the provision of a two transistorignition system for use in a positive ground electrical system and whichincludes an output transistor in series with an ignition coil, and whichfurther includes a coupling transistor with the base and emitter thereofconnected across the breaker points and with the collector thereofconnected to the base of the output transistor to cut off the same whenthe points open.

Still another feature of the invention is the provision of a threetransistor ignition system for use in a positive ground electricalsystem and which includes a pair of output transistors series connectedwith the ignition coil and which further includes a coupling transistorwith the base and emitter thereof connected across the breaker pointsand with the collector thereof connected to a bias circuit for theoutput transistors to cut off the same when the points open.

In the drawing:

FIG. 1 is a schematic diagram of a circuit constructed. in accordancewith the invention; and

FIG. 2 is a schematic diagram of an alternative embodiment of theinvention.

In accordance with the invention, an electronic ignition systemutilizing PNP transistors is provided for use in a positive groundelectrical system. A coupling transistor is used to couple the breakerpoints to the output transistor or transistors in order to attain theproper switching sequence. In one embodiment of the invention, twooutput transistors are connected in series with the high voltageignition coil. A bias circuit is provided biasing the output transistorsto be normally conducting. A coupling transistor has its output circuitconnected to the bias circuit for the output transistors so that when itconducts the output transistors are cut on. The input circuit for thecoupling transistor is connected across the breaker points such thatwhen the breaker points are closed, the coupling transistor is cut offand when the breaker points are opened, the coupling transistor isturned on. In an alternative embodiment of the invention, only a singleoutput transistor is used in series with the high voltage coil and theoutput of the coupling transistor is connected di rectly to the base ofthe output transistor.

Referring now to FIG. 1, a storage battery 11 has its positive terminaldirectly connected to ground and its negative terminal is connectedthrough an ignition switch 13 to the primary winding 15 and Secondarywinding 17 of a high voltage ignition coil 19. A ballast resistor 20 maybe included in series with switch 13. The opposite end of secondarywinding 17 is connected to a distributor (not shown) for the internalcombustion engine. The opposite end of primary winding 15 is connectedin series with a pair of output transistors 21 and 23. The emitterelectrode 25 of transistor 23 is connected through a diode 27 to ground.Diode 27 improves the switching action of the circuit and may beeliminated and satisfactory results will still be obtained. Resistors 29and 31 forward bias transistors 23 and 21 respectively, and also help totemperature stabilize these transistors at elevated temperatures. Biaspaths are completed through resistor 39 and ignition switch 13 fortransistor 23, and through the emitter collector path of transistor 23;resistor 31, diode 41, resistor 37, and ignition switch 13 fortransistor 21.

It will be apparent that transistors 21 and 23 are biased to be normallyconducting, and as a result a field is established in primary Winding 15of ignition coil 19. Secondary winding 17 of ignition coil 19 has asubstantially greater number of turns than the primary winding 15.Accordingly, there is a large step up of voltage through the transformeraction of coil 19. In the event that transistors 21 and 23 are cut off,the collapsing field in the primary winding of transformer 19 willinduce an extremely high voltage in secondary winding 17 which may beapplied through the distributor to the cylinders of the internalcombustion engine.

Unequal values of resistors 37 and 39 make a correction for difierencesin voltages potential to ground between the bases of transistors 21 and23, to thereby balance the saturation voltages of the transistors duringconduction. Zener diodes 35 and 41 protect transistors 21 and 23 fromexcessive voltages in the reverse direction induced by the collapsingfield in the primary 15 of ignition coil 19. These zeners 35 and 41 willbreak down at a voltage below the breakdown voltage of transistors 21and 23. As an alternative, zener diodes might be connected acrossemitter-collector electrodes of transistors 21 and 23, or an additionalzener diode might be connected across base-collector electrodes oftransistor 23. Diode 41 prevents the source voltage from forward biasingthe emitter to base circuit of transistor 23 during the period in whichtransistor 43 is conducting, as will be explained. A negative groundignition system using a pair of output switching transistors connectedin this manner is shown and described in the application of Madland,Serial No. 124,585 allowed January 14, 1965, and assigned to theassignee of the present invention.

A pair of breaker points 44, operable in timed relation with theinternal combustion engine, are shown as in positive ground systems,with one terminal grounded. If a proper timing sequence is to bemaintained when incorporating transistors in the system, the transistors21 and 23 should conduct when the points are closed and be cut off whenthe points are opened. Direct connection of points 44 to transistors 21or 23 would result in the opposite sequence. To retain the desiredsequence, a coupling transistor 43 is used.

The emitter to collector path of transistor 3 connects the groundterminal with the base 45 of transistor 23. A bias circuit fortransistor43 is comprised of resistors 47 and 49 which form a voltage dividernetwork from ground through switch 11 to the negative side of battery13. The base 51 of transistor 43 is connected to the juncture betweenresistors 47 and 49, and also to one contact 53 of breaker points 44.The opposite contact 54 of breaker points 44 is grounded, and thepoints, which are operable in timed relation with the internalcombustion engine, alternately open and close the path thereacross ateach firing, as is well known in the art.

It will be apparent that when breaker points 44 are closed, transistor43 will be biased to cut off, since the base '51 thereof will be atground potential, the same potential as the emitter electrode thereof.Current flow through resistor 29 and resistor 39 will forward biastransistor 23, causing it to conduct through resistor 31, diode 41, andresistor 37. This forward biases transistor 21, causing current flowthrough the primary winding 15 of transformer 19. When breaker points 44are open, current flow through resistor 47 will forward bias transistor43 into conduction, raising the potential at the base of transistor 23to ground and cutting off transistor 23. Since there will be no currentflow through resistor 31, transistor 21 will likewise be cut offimmediately, thereby causing the collapsing field in the primary winding15 of transformer 19 to produce the necessary high voltage in thesecondary winding 17 thereof. The proper timing sequence is present,since transistors 21 and 23 are conducting only when breaker points 44are closed, and are cut off when breaker points 44 open.

Referring now to FIGURE 2, a single output transistor 61 is shown seriesconnected with primary winding 15 of transformer 19. A resistor 63 inconjunction with resistor 65 provides forward bias for transistor 61.The

collector electrode 46 of transistor 43 is connected directly to thebase 67 of transistor 61 and accordingly, when transistor 43 conducts,transistor 61 will be biased to cut off.

Transistor 43 is biased by resistors 47 and 49 to be conductive whenbreaker points 44 are open. When points 44 are closed, the groundpotential will be placed on the base 51 of transistor 43 cutting offtransistor 43 and permitting current flow through resistor 63 and base67 of transistor 61. This forward biases transistor 61 into conduction,causing current flow through the primary winding 15 of transformer 19.Upon opening of points 44, transistor 43 once again becomes conductive,cutting off transistor 61 and causing the desired voltage collapse inprimary winding 15. It might be desirable under certain conditions toconnect a zener diode across the base and collector, or emitter andcollector, of transistor 61 to protect the same from high reversevoltages.

It may therefore be seen that the invention provides an improvedelectronic ignition system for internal combustion engines havingpositive ground electrical systems. The system may be directly installedin a conventional positive ground electrical system without extensivemechanical alterations. Furthermore, the system utilizes PNP transistorswithout the need of a plus transformer to reverse the timing sequence.

What is claimed is:

1. An ignition system for intermittently energizing a high voltageignition coil for an internal combustion engine having a positive groundelectrical system, including in combination, a common emitter transistorswitching means connected in series with the ignition coil, a biascircuit connected to said transistor swtiching means and basing the sameto be normally conducting, a timing circuit for causing intermittentconduction of said transistor switching means and including breakermeans having a common contact and closeable in timed relation with theinternal combustion engine, a coupling transistor, and an input circuitfor said coupling transistor connected to said timing circuit forcontrolling the conduction of said coupling transistor in response toopening of said breaker means, said coupling transistor further havingan output circuit connected to said bias circuit and causing the same tobias said transistor switching means to cut off said transistorswitching means conducting when said breaker means are closed and beingcut off when said breaker means open to cause the ignition coil todevelop a high voltage firing pulse.

2. An ignition system for intermittently energizing a high voltageignition coil for an internal combustion engine having a positive groundelectrical system, including in combination, common emitter transistorswitching means connected in series with the ignition coil, a biascircuit connected to said transistor switching means and biasing thesame to be normally conducting, a pair of breaker points for causingintermittent conduction of said transistor switching means and having acommon contact and closeable in timed relation with the internalcombustion engine, a coupling transistor having base, emitter andcollector portions, said base and emitter portions being connectedacross said breaker points, means biasing said coupling transistor intoconduction upon opening of said breaker points, said coupling transistorfurther having an output circuit connected to said bias circuit andcausing the same to bias said transistor switching means to cut ofi?when said coupling transistor is conductive, said transistor switchingmeans thereby conducting when said breaker points are closed and beingcut off when said breaker points open to cause the ignition coil todevelop a high voltage firing pulse.

3. An ignition circuit for intermittently energizing a high voltageignition coil for an internal combustion engine having a positive groundelectrical system with a pair or" intermittently operable breaker pointshaving a common side, said ignition circuit including in combination,common emitter transistor switching means connected in series with theignition coil, a bias circuit connected to said transistor switchingmeans and biasing the same to be normally conducting, a timing circuitfor connection to the breaker points to cause intermittent conduction ofsaid transistor switching means, and transistor coupling means having aninput circuit connected to said timing circuit and biasing saidtransistor coupling means into conduction upon opening of the breakerpoints, said transistor coupling means further having an output circuitconnected to said bias circuit and causing the same to bias saidtransistor switching means to cut off in response to conduction of saidtransistor coupling means, said transistor switching means therebyconducting when the breaker points close and being cut oil? when thebreaker points open to cause the ignition coil to develop a high voltagefiring pulse.

4. An ignition circuit for intermittently energizing a high voltageignition coil for an internal combustion engine having a positive groundelectrical system with a pair of intermittently operable breaker pointsone side of which is grounded, said ignition circuit including incombination, common emitter transistor switching means adapted to beconnected in series with the ignition coil, a bias circuit connected tosaid transistor switching means for biasing the same to be normallyconducting, a coupling transistor having, base, emitter and collectorportions, said base and emitter portions being adapted for connectionacross the breaker points, means connected to said coupling transistorfor biasing the same into conduction upon opening of the breaker points,said collector portion of said coupling transistor being connected tosaid bias circuit and causing said transistor switching means to be cutoff when said coupling transistor is conductive, said transistorswitching means thereby conducting when the breaker points are closedand being cut ofi when the breaker points open to cause the ignitioncoil to develop a high voltage firing pulse.

5. An ignition circuit for intermittently energizing a high voltageignition coil for an internal combustion engine having a positive groundelectrical system with a pair of intermittently operable breaker pointsone side of which is grounded, said ignition circuit including incombination, first and second switching transistors having base, emitterand collector portions with said emitter portion of said firsttransistor being connected to said collector portion of said secondtransistor, means adapted to connect said emitter portion of said firsttransistor to ground, means adapted to connect said collector portion ofsaid second transistor to the high voltage ignition coil, first biasmeans connected to said first transistor for forward biasing the same,second bias means connected to said second transistor for forwardbiasing the same and being energizable upon conduction of said firsttransistor, a third transistor having base, emitter and collectorportions with said collector portion being connected to said baseportion of said first transistor and said emitter portion adapted forconnection to ground, a bias circuit connected to said third transistorfor biasing the same conductive, and means adapted to connect said baseand emitter portions of said third transistor across the breaker pointsto cut off said third transistor upon closure of the breaker points,said third transistor serving to cut off said first transistor and saidsecond transistor when rendered conductive by opening of the breakerpoints to cause the high voltage ignition coil to develop a firingpulse.

6. An ignition circuit for intermittently energizing a high voltageignition coil for an internal combustion engine having .a positiveground electrical system with a pair of intermittently opening breakerpoints, said ignition circuit including in combination, a firsttransistor having emitter, base and collector portions, said collectorportion being adapted for connection to the high voltage ignition coiland said emitter portion being adapted for connection to ground, a biascircuit connected to said first transistor for forward biasing the same,a second transistor having base, emitter and collector portions, saidcollector portion of said second transistor being connected to said baseportion of said first transistor, said emitter portion of said secondtransistor being adapted for connection to ground, a bias circuitconnected to said second transistor for forward biasing the same, andmeans adapted to connect said base and emitter portions of said secondtransistor across the breaker points to hold said second transistor cut0E upon closure of the breaker points to permit conduction of said firsttransistor, opening of the breaker points thereby permitting conductionof said second transistor to cut off said first transistor and cause theignition coil to develop a high voltage firing pulse.

7. An ignition circuit for intermittently energizing a high voltageignition coil for an internal combustion engine having a positive groundelectrical system with a source of negative potential and with a pair ofintermittently openable breaker points, said ignition circuit includingin combination, first and second transistors each having emitter, baseand collector portions, means adapted to connect the emitter tocollector paths of said first and second transistors in series betweenground and the ignition coil to form an energizing circuit therefor, abias circuit including resistance means connected respectively acrosssaid base and emitter portions of said first and second transistors forforward biasing the same and also including further resistance meansconnecting said base portion of said first transistor to the source ofnegative potential, a third transistor having base, emitter andcollector portions, means adapted to connect said emitter portion ofsaid third transistor to ground, means connecting said collector portionof said third transistor to said base portion of said first transistorto bias said first transistor to cut off when said third transistor isconductive, thereby opening said energizing circuit, a bias circuitconnected to said third transistor for forward biasing the same, andmeans adapted to connect said base and emitter portions of said thirdtransistor across the breaker points to hold said third transistor cutoiT when the breaker points are closed and to cause said thirdtransistor to conduct when the breaker points are open, thereby cuttingoft said energizing circuit to cause the ignition coil to develop a highvoltage firing pulse.

References Cited by the Examiner UNITED STATES PATENTS 2,878,298 3/1959Giacoletto 123l48 MARK NEWMAN, Primary Examiner.

RICHARD B. WILKINSON, Examiner.

1. AN IGNITION SYSTEM FOR INTERMITTENTLY ENERGIZING A HIGH VOLTAGEIGNITION COIL FOR AN INTERNAL COMBUSTION ENGINE HAVING A POSITIVE GROUNDELECTRICAL SYSTEM, INCLUDING IN COMBUSTION, A COMMON EMITTER TRANSISTORSWITCHING MEANS CONNECTED IN SERIES WITH THE IGNITION COIL, A BIASCIRCUIT CONNECTED TO SAID TRANSISTOR SWITCHING MEANS AND BASING THE SAMETO BE NORMALLY CONDUCTING, A TIMING CIRCUIT FOR CAUSING INTERMITTENTCONDUCTION OF SAID TRANSISTOR SWITCHING MEANS AND INCLUDING BREAKERMEANS HAVING A COMMON CONTACT AND CLOSEABLE IN TIMED RELATION WITH THEINTERNAL COMBUSTION ENGINE, A COUPLING TRANSISTOR, AND AN INPUT CIRCUITFOR SAID COUPLING TRANSISTOR CONNECTED TO SAID TIMING CIRCUIT FORCONTROLLING THE CONDUCTION OF SAID COUPLING TRANSISTOR IN RESPONSE TOOPENING OF SAID BREAKER MEANS, SAID COUPLING TRANSISTOR FURTHER HAVINGAN OUTPUT CIRCUIT CONNECTED TO SAID BIAS CIRCUIT AND CAUSING THE SAME TOBIAS SAID TRANSISTOR SWITCHING MEANS TO CUTT OFF SAID TRANSISTORSWITCHING MEANS CONDUCTING WHEN SAID BREAKER MEANS ARE CLOSED AND BEINGCUT OFF WHEN SAID BREAKER MEANS OPEN TO CAUSE THE IGNITION COIL TODEVELOP A HIGH VOLTAGE FIRING PULSE.